In many wireless communication systems, a frame structure is used for data transmission between a transmitter and a receiver. For example, the IEEE 802.11 standard uses frame aggregation in a Media Access Control (MAC) layer and a physical (PHY) layer. In a typical transmitter, a MAC layer receives a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information such as a source address (SA) and a destination address (DA). The MPDU is a part of a PLCP (Physical Layer Convergence Protocol) Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to attach a PHY header (i.e., a PHY preamble) thereto to construct a PLCP Protocol Data Unit (PPDU). The PHY header includes parameters for determining a transmission scheme including a coding/modulation scheme.
An IEEE 802.11n specification (IEEE P802.11n/D1.0 (March 2006), “Amendment: Wireless LAN MAC and PHY specifications: Enhancement for Higher Throughputs”), incorporated herein by reference, provides an aggregation scheme called A-MPDU (Aggregate-Medium Access Control (MAC) Protocol Data Unit). As shown in FIG. 1, the purpose of an A-MPDU 10 is to aggregate multiple MPDUs 12 together and to transport them from a sender to a receiver in a single PLCP Service Data Unit (PSDU) 14.
FIG. 2 shows an example communication sequence 20 wherein an A-MPDU 22 is transmitted from a sender (transmitter) to a receiver, over a wireless channel. The sender transmits multiple data MPDUs 24 in an A-MPDU 22 followed by a block acknowledgement request (BAR) frame 26. On receipt of the A-MPDU 22 and the BAR 26, the receiver generates a block acknowledgement (BA) frame 28 in response and transmits the BA 28 to the sender over the wireless channel. The BA 28 indicates the receipt status of each MPDU in the received A-MPDU.
In general, both the BAR and BA frames have a subfield providing a Traffic Identifier (TID) for data MPDUs. There is a one-to-one mapping between a TID and a BAR frame. There are 16 possible TID values, in which 8 identify as prioritized Traffic Categories (TC) and the other 8 identify as parameterized Traffic Streams (TS).
FIG. 3 shows an example communication sequence 30 for aggregating 16 data MPDUs 32 in an A-MPDU 34. The sender sends 16 BAR frames 36, one per TID. The receiver generates 16 BA frames 38, one per TID. FIG. 4 shows a multiple TID BAR (Multi-TID BAR (MTID)) frame 40, and FIG. 5 shows the details of a BAR control field 42 in the Multi-TID BAR frame format 40. Table 1 below presents the meaning of different fields of the BAR control frame of FIG. 5.
TABLE 1BAR Control Field MeaningBARMulti-TIDCompressed BAframe variantComment00SimpleBlockACKReq01CompressedNo fragmentationBlockACKReq10Reserved11Multi-TIDNo fragmentationBlockACKReqACK Policy0NormalAcknowledgement1No AcknowledgementTID_INFOWith the Multi-TID BlockACKReq, the meaningof this field is to indicate the number ofTIDs + 1
FIG. 6 shows the details of a Per TID Info field 44 in the Multi-TID BAR frame format 40. FIG. 7 shows the details of a Multi-TID BA frame 50, and FIG. 8 shows the details of a BA control field 52 in the Multi-TID BA frame 50.
In the above approaches, the receiver generates multiple (immediate) BA frame responses for different TIDs, wherein the BA frame responses are transmitted back to the sender. There is a one-to-one mapping between a TID and a BA frame. This leads to processing complexity and channel bandwidth waste. As such, there is need for an acknowledgment scheme that dispenses with the need to send multiple block acknowledgments, one per TID, from a receiver to a sender.